Thermal mineral piercing method and apparatus



G. H. SMITH ET AL April 20, 1954 THERMAL. MINERAL PIERCING METHOD AND APPARATUS 2 Sheets-Shet 1 Filed March 25, 1948 M s N R wa Y 8 1 m mm m 5 5 H.5 /m R N T 57 wwwmm 0 K 12/ 2 mhi n A H J A EVM v L H m m m m GMWJ April 20, 1954 G. H. SMITH ET AL 2,675,994

THERMAL MINERAL PIERCING METHOD AND APPARATUS Filed March 25, 1948 2 Sheets-Sheet 2 I 51% g BEVERLY M. H/GG/NBOTHAM WILLIAM J. TCHELL JOSEPH J. AMA/V ATTORNEY Patented Apr. 20, 1954 THERMAL MINERAL PIERCING METHOD AND APPARATUS George H. Smith, Beverly M. Higginbotham, William J. Mitchell, and Joseph J. Calaman, Kenmore, N. Y., assignors, by mesne assignments, to Union Carbide and Carbon Corporation Application March 25,1948, Serial No. 17,074

This invention relates to a novel method and apparatus for thermally piercing holes in minerals and mineral-like materials.

Holes have been successfully pierced in masses of minerals and mineral-like materials by applying thereto a flame from a blowtorch to separate material from the mass, removing the separated material from the mass to form a hole, and advancing the blowtorch into successive portions of the hole as they are formed to increase its depth. Some rocks, such as quartzite, have been pierced by a spalling process wherein particles of rock are spalled off without fusion and are blown out in an unfused condition. Others, such as iron ore, have been pierced by a process wherein the ore is melted and then either blown out in the melted condition or, preferably, quenched with water in the hole, mechanically disintegrated by the physical impact of rotating teeth, and blown from the hole in a solid condition.

When piercing holes in such materials with a blowtorch it has sometimes been difficult to extend the holes to a great depth, especially when the holes are of large diameter such as seven inches or more. This difliculty has been due in large part to insuffioient clearance forp ssage of the blowtorch when the hole is not concentric with the torch or when projections or cores are left in the hole.

Among the objects of the invention are to provide a novel method and apparatus for piercing in a mass of rock or the like a hole concentric with the blowtorch; and to provide such a method and apparatus for insuring sufficient clearance for the blowtorch even when piercing holes of great diameter, such as greater than seven inches, and great depth, such as 30 feet. Another object is to provide a blowtorch which is so constructed as to supply fluids to the blowtorch nozzle without leakage when the nozzle is rotated relatively to fluid supply conduits. Other objects are to provide anovel construction whereby a piercing blowtorch can be suspended while its nozzle rotates; and whereby the blowtorch nozzle can be rotated While it is advanced downwardly into a hole. Still other objects are to provide a blowtorch having slag disintegrating teeth which are removable and replaceable at will; and to pro- 3 vide such a blowtorch having a plurality of long tubes, and means to compensate for differential thermal expansion of the tubes.

The above and other objects, and the novel features of the invention, will become apparent from the following description, having reference to the accompanying drawings, wherein 22' Claims. (crass-4.8)

2 Fig. 1 is a vertical mid-sectional view of the upper portion of a novel blowtorch in accordance with the invention, down to a transverse break linea-a;

Fig. 1a is a vertical mid-sectional view of the lower portion of the same blowtorch, extending down from the transverse break line Fa; Y

Figs. 2 and 3 are cross-sectional views taken along the lines 2--2 and 33 in Fig. 1;

Fig. 4 is a cross-sectional view taken along the line 44 in Fig. 1a;

Fig. 5 is an elevational view of the lower end of the blowtorch, partly broken away, as seen from the line 5-5 in Fig. 1a; and

Fig. 6 is a longitudinal sectional view of the lower or discharge end of another form of blowtorch embodying the principles of the invention.

In accordance with this invention, there is provided a novel method for thermally piercing a hole of large diameter in a mass of mineral or mineral-like material which method comprises directing flame from a blowtorch against the mass in such a way as to impinge on a continuous area extending from the projected longitudinal axis of the blowtorch radially to a position beyond the extended periphery of the greatest diameter portion of the blowtorch expected to enter the hole. The flame is rotated about the longitudinal axis while advancing the blowtorch into the initially formed circular hole to deepen it, thereby heating and separating material from the mass over the whole of a circular area substantially greater in diameter than the blowtorch. .In this way, adequate clearance for the passage of the blowtorch is providedat the sides of the hole, and no cores or projections are left which might sto the advance of the blowtorch.

For performing the method described briefly above, there is provided a novel mineral-piercing blowtorch comprising a body B having an inlet for fluid, a fluid conduit or tube W journalled at its upper end on the body B for rotation relatively thereto, and a nozzle or heating head N secured to the lower end of conduit W and rotatable therewith. Oxygen and fluid fuel are supplied to nozzle N through supply conduits or tubes 0 and F, respectively. A plurality of radial teeth T are carried on the nozzle N for rotation therewith, to. break up detritus in a hole being pierced and to ream the sides of the hole. The nozzle N has one or more suitable flame ports for directing below the nozzle a heating flame which spreads radially from the center of the hole to a point well beyond the extended periphery of that part of the blowtorch in the hole. As the nozzle rotates, the flame also rotates about the longitudinal axis of the blowtorch thus sweeping over and uniformly heating the whole of a circular area on the mineral material concentric with the nozzle and of greater diameter than the nozzle with teeth, thus providing a circular hole large enough to accommodate the blowtorch. It is advantageous, especially for holes of large diameter, that at least part of the heating flame be discharged from the nozzle eccentrically, since in this way a larger area is heated than would be possible if only a single flame of the same size were discharged concentrically.

More specifically in accordance with the present invention, the nozzle N comprises an adaptor body I I over the outside surface of which is threaded a removable and replaceable sleevcl3 carrying several longitudinally extending radial disintegrator teeth T equally spaced about its periphery. A flame tip i5 is threaded into a bore I! in the bottom of the adaptor body and, has a flange 19 which overlies and abuts against'the lower end of the adaptor body. lhe upper end of the adaptor body H is threaded over the lower end of the outside conduit W to receive water, which enters a bore 2| and flows through a pair of ducts 23 in the adaptor body H to its bottom face. Flame tip l5 has an annular water distributing chamber 25 in the upper surface of the flange l9 which registers with the ducts 23 and conducts water to a plurality of radial water discharge ports 21 which deliver water jets near the lower ends of teeth T for quenching any molten slag and for dampening detritus.

At its upper end the conduit W is secured by bolts 29 to a flange 3| on the lower end of a core 33 which is rotatably mounted in a bore 35 within a barrel 3! constituting the outside portion of the body B. Core 33 is retained within barrel 3'! at the top by a nut 39 threaded on the top of the core and resting on an annular bearing plate 4| on the top of the barrel, and at the bottom is retained by the flange 3| which overlies the bottom surface of the barrel.

Water is supplied to the inside of conduit W by a water supply pipe 43 threaded into a radial inlet bore 44 near the lower end of barrel 31. From pipe 43 the water passes to an annular distributing chamber 45 in the internal surface of the barrel, and thence flows through a pair of radia1 ducts 4'! in core 33 to a pair of longitudinal passages 49 which extend downwardly to the lower end of the core andv open into the conduit W. Barrel 31 is held against rotation by the supply pipe 43 and as the core, 33 rotates within the barrel, ducts remain in register with chamber 45 and water is continuallycarriedv to the conduit W and the nozzleN for cooling the blowpipe before it is discharged from ports 21. It is obvious that the distributing. chamber 45 could as well be formed in the external surface of .core 33, or could be formedhalf in the-core and half in the barrel. U a i The tip also is provided with a ring of oxygen discharge ducts 5| "which are, supplied with oxygen by the second conduit or tubeO arranged concentrically within conduitW. Conduit O is secured at its lower end, as by brazing, to the adaptor body I I where it opens into the bore [1, and is secured at its'upper end, as by brazing, within a central bore 55 in the core 33. Oxygen is supplied -to the conduit 0 from an oxygen supply pipe 5'! threaded into a radial bore 58 near the upper endof barrel 3'! and opening into an annulardistributing chamber 59 formed in the internal surface of the barrel. Oxygen passes from the annular chamber 59 into the bore 55 during rotation of the core 33, by way of a radial duct 5|, which registers continually with the annular chamber.

When the blowtorch of the invention is positioned within a deep hole, the heat of the flame tends to cause the outside conduit W to expand considerably while the internal conduit 0 remains relatively cool. Since the inside conduit 0 is fixed at both ends, it is necessary to compensate for the differences in the thermal expansion and contraction of the two conduits by providing means to permit expansion and contraction of the inside conduit while maintaining tight seals at both of its ends. This is accomplished advantageously by providing an expansible and contractible bellows 63 as an integral partof conduit O at its upper end.

Fuel is supplied to a central discharge passage 65 arranged in tip I5 concentrically with the ring of oxygen discharge ducts 5!, by the central supply tube F threaded at its lower end into a bore 68 in the tip and extending upwardly concentrically through the oxygen tube 0 through the bore 55 in core 33. Tube F projects at its upper end above the top of the core 33 and is coupled by a swing joint 59 of conventional construction to a fuel supply pipe II in such a way that while the fuel tube F rotates with the nozzle N, fuel is continually supplied to the upper end of the tube. To prevent leakage of oxygen from the upper end of core 33 past the fuel tube F, packing 13 is held tightly in the space between the fuel tube and the wall of bore 55 by a gland l5 retained by a gland nut 11 which is threaded over the top of the core. Differential expansion of the two conduits W and F is compensated for by lengthwise movement of tube F in the packing 13 and gland 15.

Since the blowtorch described above may be. of great length, often being longer than 30 feet, concentricity of the fuel tube F, the oxygen conduit O, and the water conduit W is maintained by suitable spacers. As shown in Fig. 1a, two sets of radial spacers F9 are welded to the central fuel tube F at longitudinally spaced points so that they engage the inside surface of the oxygen conduit 0. Similarly, radial spacers 8| are Welded to the outside surface of theoxygen conduit 0 near its upper end and engage the inside surface of the water tube W.

In order to permit core 33 to rotate freely within barrel 31, ball bearings are provided between the core and barrel both above and below each of the supply pipes 43 and .57. For installation and servicing of the bearings the barrel .31. is composed ofannpp-er. section 83 andv a separate adjoining lower section 85, andeach section has sockets at itsupperand lower ends toreceive the bearings. Likewise, in order to prevent the leakage of fiuid through the'space betweenthe core 33. and the barrel 31', suitable. packings are provided' between these members on both sides of the supply pipes 5'! and 43.

As shown in Fig. 1', the packing and the bearing below the water inlet pipe 43 are provided by inserting an annular packing disc 81 within the space between the core 33 and the lower barrel section 85 and holding it in place with a bushing 89 threaded into a bore 9|. Below bushing 89 a ball bearing 92 is inserted within a counter bore 93 in such a way that the inner race of the bearing fits snugly over core 33 and is rotatable therewith, while the outer race of bearing 92 fits snugly with the wall of the counterbore and is held stationary. A similar construction for the packings and bearings above the watersupply pipe 43, and both below and above the oxygen supply pipe 5'I, is employed.

A blowtorch of the great siz and weight required for piercing deep holes in mineral materials, for example, holes 30 feet deep and 9 inches in diameter, cannot be handled manually. Therefore the torch is provided with a non-rotating supporting collar 91 surrounding and engaging the outside conduit W below the barrel 3'I, and constituting a bearing within which the conduit W rotates during the piercing of a hole. Between collar 9'! and conduit W there is a pair of ball bearings IOI and I 02 resting on a shoulder 98 and facilitating rotation of the conduit in the collar. Collar 91 is retained in position on the conduit W by a second shoulder formed by a retaining nut 99 threaded over the outside of the conduit and abutting against the top hearing ,I A :bail I03 is secured to the collar 91 for suspending the blowtorch from a cable duringthe piercing of a hole.

The rotating parts of the blowtorch are driven by a driving mechanism such as a motor-driven gear I04 rotating a horizontal table I05 having a hexagonal hole I06 receiving a hexagonal drive bushing I0I. Drive bushing I0! is secured to the outsid conduit W of the blowtorch by a plurality of cylindrical keys I09 which fit within longitudinal grooves or keyways I II in the external surface of the outside conduit W and within corresponding grooves H3 in the inside surface of the drive bushing. With this construction the drive bushing I01 and keys I 09 are freely movable lengthwise of the blowtorch but cannot rotate on the outside conduit W. Therefore, as the depth of a hole being pierced increases, the blowtorch can be lowered through the drive bushing I0'I while the latter continues to transmit motion from table I05 to the lblowtorch.

In the operation of the blowtorch described in detail hereinabo-ve, deep holes are pierced vertically downward in a body of mineral material, such as iron ore, by discharging oxygen and a combustible fluid such as kerosene from the tip I 5 to mix together below the tip and form upon combustion a flame of the diffusion type which melts the mineral material and forms a. fluid slag. Th hot gases of combustion force the fluid slag out of the melting zone and upwardly to a position such that water jets from the ducts 21 strike the slag, quench it, and at least partially solidify it. The quenched and solidified slag is then mechanically disintegrated by the rotating teeth T, and the disintegrated slag particles are blown upwardly in a solid=condition around the blowtorch to the top of the hole, by the gaseous products of combustion and the steam formed by evaporation of water in the hole. As the hole becomes deeper, the blowtorch is lowered to maintain a substantially. constant spacing of the nozzle N from the bottom of the hole. This can be accomplished "inany suitable way, as by lengthening the cable which is secured to: th bail I03.

When a hole of relatively large diameter such as seven inches or greater is to be pierced, the I oxygen and fuel are discharged from the nozzle in such a way as to produce an ec'centrically located flame which sweeps over a large circular area during rotation of the nozzle. Even when a substantially axially directed flame is used, as

for piercing holes of smaller diameter such as about three inches, any inaccuracy which might cause eccentric discharge of the flame from the tip is compensated for by rotation of the nozzle during the piercing of a hole.

When the mineral mass being pierced is of a. type which is wholly or partially heat-spallable, the spalled off particles in the unfused condition are merly dampened bythe water from ports 27 and then blown from the hole.

When teeth A are worn or when a different type of teeth is wanted for any operation, sleeve I3 can be removed from adaptor body I I and replaced by another sleeve having the proper teeth. Also when flame tip I5 is damaged, or when a difierent type of flame is desired, it can be threaded out of bore I1 and replaced by a suitable new tip.

Fig. 6 shows another type of blowtorch nozzle N that can be used in place of the nozzle N shown in Figs. 1 and la. Nozzle N is designed with an internal combustion chamber I I3 into which fluid fuel and combustion-supporting gas are injected from passages H5 and 1, respectively. Upon combustion of the fuel in chamber II3 an axial flame is discharged from the nozzle through an axial passage H9; and a second flame is discharged eccentrically from the nozzle through a second passage I2I that makes an angle of-about degrees With the longitudinal nozzle axis. With this flame pattern, a continuous area of rock is heated extending radially from the cen ter of a hole, marked by the extended longitudinal axis of the blowpipe, to a position well beyond the periphery of the disintegrator teeth I23. Water for cooling and for quenching slag is supplied through an outside conduit I25 and is discharged from nozzle N through a plurality of circumferentially arranged ports (not shown).

Using a nozzle N of the type shown in Fig. 6, having a diameter of six inches, a hole 30 feet deep and between eight and nine inches in diameter was successfully pierced at a rate of 27.5 feet per hour in the stratified taconite ore of the upper cherty division of the Biwabick iron ore formation of the Mesabi Range by melting, quenching, and mechanically disintegrating the ore. Kerosene was used as the fuel and oxygen as the combustion-supporting gas.

In contrast, when an attempt was made under the same conditions, but with a nozzle discharging only an axial flame,no progress could be made. Also under the same conditions, but using a nozzle discharging a single flame at an angle of 20 degrees to the longitudinal axis, a hole three feet deep and seven inches in diameter was pierced at a rate of only nine inches per minute, and the hole could not be extended deeper than three feet because a crown of ore formed in its center and impeded the blowtorch.

Specific embodiments of our novel blowtorch have been described hereinabove by way of i1lustration only. It is to be understood that changes in the construction and arrangement of parts, and in the method of operation, can be eifected by persons skilled in the art.

We claim:

1. In a blowtorch, a body having an inlet for fluid; a fluid conduit journalled at one end on said body for rotation relatively thereto; said body having passage means so constructed and arranged as to maintain communication between said inlet and said conduit during rotation of said conduit; and a heating flame head secured to the opposite end of said conduit and rotatable therewith-said flame hea having port me'ansfin an external surface thereof for discharging such fluid therefrom.

2. In a blowtorch, a body having an inlet for fluid; a fluid conduit journalled at one end on said body for rotation relatively thereto; said body having passage means so constructed and arranged as to maintain communication between said inlet and said conduit during rotation of said conduit; and a heating nozzle secured to the opposite end of said conduit and rotatable therewith, said nozzle having a flame port so constructed and arranged as to project flame eccentrically therefrom.

3-: In 'a blowtorch in accordance with claim 1, a supporting collar on said conduit separate from said body and head, said collar constituting a bearing within which said conduit rotates.

4. In a blowtorch, a barrel member having an internal peripheral surface; a core member rotatably mounted in said barrel member and having an external peripheral surface adjoining said internal surface; a heating flame nozzle spaced from said core member and ,having port means in an external surface thereof for discharging fluid therefrom; a conduit secured to both said core member and said nozzle whereby said core member, conduit, and nozzle are rotatable together as a unit; said barrel member having a first inlet for fluid; said core member having a first duct extending to the inside of said conduit for supplying fluid to said conduit; and one of said members having a first annular chamber in one of said adjoining surfaces communicating with both said first inlet and said first duct during rotation of said core in said barrel.

5. In a blowtorch in accordance with claim 4, packing between said external peripheral surface of said core and said internal peripheral surface of said barrel on both sides of said annular chamber preventing fluid leakage during r tation of said core.

6. In a blowtorch in accordance with claim 5, bearings between said core and said barrel facilitating rotation of said core. I

7. In a blowtorch in accordance with claim 8, said barrel member comprising separate a'djoin ing upper and lower sections; said blowtorch comprising bearings and packings between said core and said barrel in each of said sections on both sides of each of said annular chambers.

8. In a blowtorch in accordance with claim 4, a tube within said conduit connected to both said core member and said nozzle and'rotat able' therewith; said bai' rel member having a second inl'et for fluid spacedhfr'om said first-inlet; saidcore member having 'a-second duct extending to' the inside of said" tube; and one-of said membershav ing a second annular chamber in one of said-adj oining surfacescommunicating with both' said secondinlet and said second duct during rota? use of said core member. f V f In ablowtorch in ccor ance withcl airn 8, means permitting expansion and contraction of said tube while maintaining tight s'eals b t en said tube and said core member and nozzle) I I 1Q. In a blowtorchin accordance with claim 8, a second conduit within'saidflrst-named conduit connected at one endto said'nozzle and rotatable therewith, said second conduit extending through said. ;core member; a fluid supplyconduit; and a coupl ing .between, said fluid supplyv conduit and the. top of said-,seconctponduitso constructed and arranged; as topermit said second conduit to rotate with respect to said fluid supply conduit while fluid is supplied thereto.

11. In a blowtorch, a nozzle adapted to project flame therefrom; a rotatable conduit engaging said nozzle at one end thereof; a shoulder on said conduit and a supporting collar on said conduit between said nozzle and said shoulder, said collar abutting against said shoulder and constituting a bearing'within which said conduit rotates.

12. In a blowtorch in accordance with claim 11, a bail carried by said collar for suspending said blowtorch in vertical position while said conduit rotates with respect to said collar and said bail.

13. In a blowtorch, a body having an inlet for fluid; a fluid conduit journalled at one end on said body for rotation relatively thereto; said body having passage means so constructed and arranged as to maintain communication between said inlet and said conduit during rotation of said conduit; a nozzle secured to the opposite end of said conduit and rotatable therewith, said nozzle having a flame port for projecting flame therefrom; and at least one keyway on the outside of said conduit extending approximately the full length thereof.

14. In a blowtorch, a body having an inlet for fluid; a fluid conduit journalled at one end on said body for rotation relatively thereto; said body having passage means so constructed and arranged as to maintain communication between said inlet and said conduit during rotation of said conduit; a nozzle secured to the opposite end of said conduit and rotatable therewith, said nozzle having a flame port for projecting flame therefrom; and a drive bushing gripping said conduit, the construction and arrangement being such that said drive bushing and conduit rotate together while said drive bushing is free to move on said conduit lengthwise thereof.

15. Ina blowtorch in accordance with claim 14, driving mechanism engaging said drive bushing for rotating said bushing and conduit.

16. In a blowtorch, an adaptor body;'a first tube and two other tubes within said first tube, all terminating at their front ends at said adaptor body and projecting rearwa'rdly therefrom; a supply conduit for water connected to said first tube; a supply conduit for fuel connected to one of the inside tubes; a supply conduit for combustion-supporting gas connected to the other of the inside tubes; said supply conduits and said tubes being so constructed and arranged that-said :tubes are-rotatable with respect to said supply conduits; a :nozzle tip secured. to said adaptor bodyrincommunication with said tubes,said tip being removable and replaceable at will; and teeth -;pr.o- 'ecting from" said blowtorch near the frontrend-thereof.

I 11 a=blowtor-ch-in accordance with claim '16;

said teeth being mounted-" on a sleeva said "sleeve being removable and replaceable at will on said blowtorch. a .z-18. a method of: thermally-piercinga holein amass of rock by applying thereto flame from a heating: device, separating material 'from"-sa id mass. by'said flame, removing the separated -ma terial from said mass to form adholewan'd' advanci-ng .said flame into l'successive" portions of said hole as formed toincrease thev depth thereof,

theimprovement comprising forming and directing the flame from the end of the heating device at least in part eccentrically of the longitudinal axis-of the heating device; and continuously-rd tilting-Said flame about the longitl'ldihdl aiiis- 0'1 said heating device during its advance to assure formation of a hole concentric with said heatin device.

19. In a method of thermally piercing a hole in a mass of rock by applying thereto flame from a heating device, separating material from said mass by said flame, removing the separated material from said mass to form a hole, and advancing said heating device into successive portions of said hole as formed to increase the depth thereof, the improvement comprising directing said flame from said heating device as an axial flame jet and a second flame jet at an angle to said axial flame jet in such a way as to impinge on a continuous area of said mass extending from the center of said hole radially to a position beyond the extended periphery of the greatest diameter portion of said blowtorch expected to enter said hole, and rotating said flame about the longitudinal axis of said blowtorch while advancing said blowtorch, thereby heating and separating material from said mass over a circular area concentric with and of greater diameter than said blowtorch.

20. In a method of thermally piercing a hole in a mass of rock by applying thereto flame from a heating device, separating material from said mass by said flame, removing the separated material from said mass to form a hole, and ad- Vancing said flame into successive portions of said hole as formed to increase the depth thereof, the improvement comprising projecting said flame eccentrically from said heating device and rotating said flame about the longitudinal axis of said heating device during its advance to assure formation of a hole of larger diameter than, and concentric with, said heating device.

21. In a method of thermally piercing a hole in a mass of rock by applying thereto flame from a heating device, separating material from said mass by said flame, removing the separated material from said mass to form a hole, and advancing said heating device into successive portions of said hole as formed to increase the depth thereof, the improvement comprising: directing said flame from said heating device as a plurality of flame jets, at least one of said flame jets bein directed eccentrically with respect to the longitudinal axis of said heating device, and rotating said flame jets about the longitudinal axis of said heating device while advancing said heating device, said flame jets being so directed from said heating device as to impinge on and sweep over a continuous circular area of said mass in front of, and of greater diameter than, said heatin device to heat and separate material from said mass over said circular area.

22. In a method in accordance with claim 21, said eccentrically directed flame jet diverging at an angle from the longitudinal axis of said heating device.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 719,882 Scales Feb. 3, 1903 1,438,999 Hoke Dec. 19, 1922 1,800,616 Forster Apr, 14, 1931 2,184,479 Wall et al. Dec. 26, 1939 2,234,454 Richter Mar. 11, 1941 2,286,191 Aitchison et al June 16, 1942 2,294,866 Bergmann Sept. 1, 1942 ,327,496 Burch Aug. 24, 1943 2,327,498 Burch Aug. 24, 1943 2,548,463 Blood Apr. 10, 1951 

21. IN A METHOD OF THERMALLY PIERCING A HOLE IN A MASS OF ROCK BY APPLYING THERETO FLAME FROM A HEATING DEVICE, SEPARATING MATERIAL FROM SAID MASS BY SAID FLAME, REMOVING THE SEPARATED MATERIAL FROM SAID MASS TO FORM A HOLE, AND ADVANCING SAID HEATING DEVICE INTO SUCCESSIVE PORTIONS OF SAID HOLE AS FORMED TO INCREASE THE DEPTH THEREOF, THE IMPROVEMENT COMPRISING: DIRECTING SAID FLAME FROM SAID HEATING DEVICE AS A PLURALITY OF FLAME JETS, AT LEAST ONE OF SAID FLAME JETS BEING DIRECTED ECCENTRICALLY WITH RESPECT TO THE LONGITUDINAL AXIS OF SAID HEATING DEVICE, AND ROTATING SAID FLAME JETS ABOUT THE LONGITUDINAL 